The present invention relates to a method for supplying powder to be used in a flame spray coating operation in which raw powder material (hereinafter described as powder material) is fed to a flame spray coating burner for carrying out a flame spray coating operation. That is to say, the present invention relates to a method of supplying powder material for flame spray coating which allows the rate at which the material is supplied to be easily controlled. The fuel gas and combustion supporting gas, which are directed to a burner for flame spray coating, also serve as: (1) jet gas of an ejector which acts as a carrier for supplying raw powder material to the burner; (2) suction gas which is introduced into a suction chamber of the ejector for regulating the rate at which powder is fed; and (3) gas which is directly introduced into the burner for spray coating without relation to the supply rate of raw material.
So-called spray coating operation with powder in which fine powdered metal, intermetallic compound or ceramics is heated to be formed in melting condition and is sprayed over base material to form an adherent coating has roughly been classified into two kinds of operations, that is, a flame spray coating operation and a plasma spray coating operation. The present invention, however, relates to an improvement on a method for supplying powder by making good use of an ejector employed in said flame spray coating operation.
In a conventional flame spray coating operation, it has broadly carried out control for the supply amount of powder due to a process for introducing the air into a suction chamber of an ejector in case of feeding powder material to a spray coating burner by means of an ejector. In other words, when the supply amount of powder is intended to be increased, the capacity of the air to be introduced into said suction chamber is decreased to lower down the internal pressure of said suction chamber so as to be able to transfer a large amount of powder into said suction chamber, while in case of the supply amount of powder being intended to be decreased, the capacity of the air to be introduced into the suction chamber is increased to raise up the internal pressure of the suction chamber so as to be able to decrease the supply amount of powder. Moreover, in the foregoing conventional method for supplying powder material, a large capacity of nitrogen contained in the air is mixed within flame so as to cause lowering down in the temperature of flame, moreover, oxygen contained in the air is also mixed within said flame to cause unstable balancing of combustion condition, in particular, said conventional method is not proper for flame spray coating operation with powder material such as ceramics (e.g. Al.sub.2 O.sub.3) having a high melting point by using propane, methane, Hydrogen and the like as fuel gas.